1. Technical Field
The present invention relates to a particle accelerator and a charged particle beam irradiation apparatus including the particle accelerator.
2. Description of the Related Art
A cyclotron as an accelerator accelerating charged particles is known. The charged particles accelerated in the cyclotron are, for example, used in proton beam therapy equipment in which the charged particles are emitted to a tumor of a cancer patient to treat the cancer. In addition, the charged particle accelerated in the cyclotron is used in a radioisotopes manufacturing apparatus which manufactures radioisotopes that are a raw material of radioactive drugs by irradiating a target material.
Acceleration electrodes W-shaped electrodes) for accelerating the charged particles, and electromagnets generating a magnetic field in the cyclotron are disposed inside the cyclotron. High frequency electric power is supplied from a high frequency power source (several tens of MHz to several hundreds of MHz) to the acceleration electrode.
In addition, the control of each part is performed on the assumption that a period (the time required for one revolution) of the charged particle which is accelerated in a spiral orbit inside the cyclotron, becomes constant in the cyclotron. Then, electric power having a frequency corresponding to the revolution period of the charged particle is supplied to the acceleration electrode. In other words, during the operation of the cyclotron, the frequency of the electric power supplied to the acceleration electrode is controlled so as to always be constant.
In addition, a matching circuit is disposed between the high frequency power source and the acceleration electrode. The matching circuit has a function of performing the impedance matching between the high frequency power source and the acceleration electrode. Unless there is the impedance matching between the high frequency power source that is the output side and the acceleration electrode that is input side, loss of the high frequency current that is transmitted to the acceleration electrode becomes large, and distortion and degradation of the high frequency voltage can occur. Thus, since a reflective wave is generated and superimposed in the transmitting path of the high frequency current, there is a problem in that the high frequency current is a standing wave and becomes an impediment. Accordingly the impedance matching is achieved using the matching circuit so that the occurrence of problems that could be an impediment or the like can be avoided. The matching circuit described above includes a coil as an inductance element and a capacitor as a capacitance element.